An apparatus is being developed for the determination of 1) corrected fluorescence emission spectra, 2) true excitation spectra, 3) absolute quantum yields and 4) polarizations for very weak emissions (phi f approximately 10 to the minus fifth power). This apparatus is being used to investigate a) the fluorescence characteristics of the base nucleosides and nucleotides in aqueous solution at room temperature and b) the nature of the excited state interactions in dinucleotides, oligonucleotides, polynucleotides, DNA's and RNA's.